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World Housing Encyclopedia Report

Country: El Salvador

Housing Type: Vivienda de Adobe (Adobe house)

Contributors:Manuel A. LopezJulian BommerGilda Benavidez

Primary Reviewer:Sergio Alcocer

Created on: 6/5/2002Last Modified: 6/17/2003

This encyclopedia contains information contributed by various earthquake engineering professionalsaround the world. All opinions, findings, conclusions, and recommendations expressed herein are those

of the various participants, and do not necessarily reflect the views of the Earthquake EngineeringResearch Institute, the International Association for Earthquake Engineering, the Engineering Information

Foundation, John A. Martin & Associates, Inc. or the participants' organizations.

Table of Contents

General Information............................................................................................1Architectural Features........................................................................................ 3Socio-Economic Issues...................................................................................... 4Structural Features............................................................................................. 6Evaluation of Seismic Performance and Seismic Vulnerability.......................... 10Earthquake Damage Patterns............................................................................ 12Building Materials and Construction Process..................................................... 13Construction Economics.....................................................................................15Insurance............................................................................................................16Seismic Strengthening Technologies................................................................. 17References......................................................................................................... 18Contributors........................................................................................................ 19Figures................................................................................................................20

1 General Information

1.1 CountryEl Salvador

1.3 Housing TypeVivienda de Adobe (Adobe house)

1.4 SummaryThis housing type can be found in rural andurban areas:Rural: Adobe houses are generally smallstructures, 5 m X 6 m in plan, havingload-resistant walls made of adobe bricks withthickness between 0.3 and 0.5 m. Usually, theyare single family dwelling (5 people) houses.Wood planks that support metal sheets coveredby tiles can constitute the roof. In some cases,the roof can be a thatched roof supported onwood purlins.Urban: Adobe houses are much bigger in urbanareas than in rural areas. Their plans are 15 m X30 m or bigger. One floor structures. The wallthickness can easily reach 1 m and wall heightcan reach 3 m or more.In both cases mentioned above, the adobehousing type has performed badly inearthquake; its heavy roof sometimes can be itsbiggest weakness; in addition, its unreinforcedwalls make this house vulnerable toearthquakes.

FIGURE 1: Typical Building

1.5 Typical Period of Practice for Buildings of This Construction TypeHow long has thisconstruction been practiced< 25 years< 50 years< 75 years< 100 years< 200 years> 200 years X

Is this construction still being practiced? Yes NoX

Additional Comments: This construction practice was, and still is, widely used in El Salvador although thisregion is highly seismic. El Salvador's earthquakes of 2001, and their aftershocks, mainly destroyeddwellings built with adobe; unfortunately, however, people are still using this construction type to rebuildtheir shelters.

1.6 Region(s) Where UsedThis construction practice is widespread throughout the country. San Salvador, the capital of El Salvador,is perhaps the only area where this construction type does not exist. The San Salvador Metropolitanbuilding and planning agency (OPAMSS) and the Vice Secretary of Housing (ViceMinisterio de Vivienda)

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have prohibited the construction of adobe housing due to its poor seismic performance. The ViceSecretary allows adobe houses only in regions declared as ecological areas.

1.7 Urban vs. Rural ConstructionWhere is this construction commonly found?In urban areasIn rural areasIn suburban areasBoth in rural and urban areas X

Additional Comments: This housing type is no longer permitted in urban areas.

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2 Architectural Features

2.1 OpeningsRural: Houses have four walls, two of which have openings. Openings are less than or equal to 30% ofthe wall area. The other two walls generally do not have openings.Urban: There is a number of openings in these houses. The amount of openings can be as high as 50%.

2.2 SitingYes No

Is this type of construction typically found on flat terrain? XIs this type of construction typically found on sloped terrain? (hilly areas) XIs it typical for buildings of this type to have common walls with adjacentbuildings?

X

The typical separation distance between buildings is meters

2.3 Building ConfigurationThe typical shape of a building plan for this housing type is rectangular.

2.4 Building FunctionWhat is the main function for buildings of this type?Single family house XMultiple housing unitsMixed use (commercial ground floor, residential above)Other (explain below)

Additional Comments: Some houses also include commercial space, especially in towns in urban areas.

2.5 Means of EscapeHouses have a main entrance and have exits to an internal patio in urban areas. In rural areas, houseshave two doors, each of which is located at opposite walls of the structure.

2.6 Modification of BuildingsThere is no modification from the original structure.

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3 Socio-Economic Issues

3.1 Patterns of OccupancyOne family typically occupies one house.

3.2 Number of Housing Units in a Building1 units in each building.

3.3 Average Number of Inhabitants in a BuildingHow many inhabitants reside in a typical building of thisconstruction type?

During the day / businesshours

During the evening / night

< 5 X5 to 10 X10-20> 20Other

3.4 Number of Bathrooms or Latrines per Housing UnitNumber of Bathrooms: 1Number of Latrines: 1

Additional Comments: 1 in urban areas; 1 or 0 in rural areas

3.5 Economic Level of InhabitantsEconomic Status House Price/Annual Income

(Ratio)Very poor X 350/1000Poor X 700/2500Middle Class X 12000/20000Rich /

Additional Comments: The prices are expressed in US$.

3.6 Typical Sources of FinancingWhat is the typical source of financing for buildings of this type?Owner FinancedPersonal SavingsInformal Network: friends and relatives XSmall lending institutions/microfinance institutionsCommercial banks / mortagesInvestment poolsCombination (explain)Government-owned housingOther

3.7 OwnershipType of Ownership/OccupancyRent XOwn outright XOwn with Debt (mortgage or other)Units owned individually (condominium)Owned by group or poolLong-term leaseOther X

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Additional Comments: Urban: Typically own outright. Rural: The landowners give a space to peasants tobuild their houses and to work the land. The peasants give part of their harvest to the landowner as rent.

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4 Structural Features

4.1 Lateral Load-Resisting SystemThe adobe walls that act as shear walls providing the lateral stiffness. In urban areas, the thickness of thewalls can be as much as 1 m. In rural areas, the thickness can be between 0.3 and 0.5 m. The roof canbe considered as a flexible diaphragm and is supported directly on the walls.

4.2 Gravity Load-Bearing StructureRoof loads are directly transmitted to the shear walls by wood purlins or beams. The beams directly reston the top of the walls. Walls take the entire gravity load. Walls transfer the load to the foundation.

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4.3 Type of Structural SystemMaterial Type of

Load-BearingStructure

# Subtypes

Masonry Stone masonrywalls

1 Rubble stone (field stone) in mud/lime mortar or withoutmortar (usually with timber roof)

2 Massive stone masonry (in lime or cement mortar)Earthen walls 3 Mud walls

4 Mud walls with horizontal wood elements5 Adobe block or brick walls X6 Rammed earth/Pise construction

Unreinforced brickmasonry walls

7 Unreinforced brick masonry in mud or lime mortar8 Unreinforced brick masonry in mud or lime mortar with

vertical posts9 Unreinforced brick masonry in cement or lime mortar

(various floor/roof systems)Confined masonry 10 Confined brick/block masonry with concrete posts/tie

columns and beamsConcrete blockmasonry walls

11 Unreinforced in lime or cement mortar (various floor/roofsystems)

12 Reinforced in cement mortar (various floor/roof systems)13 Large concrete block walls with concrete floors and roofs

Concrete Moment resistingframe

14 Designed for gravity loads only (predating seismic codes i.e.no seismic features)

15 Designed with seismic features (various ages)16 Frame with unreinforced masonry infill walls17 Flat slab structure18 Precast frame structure19 Frame with concrete shear walls-dual system20 Precast prestressed frame with shear walls

Shear wall structure 21 Walls cast in-situ22 Precast wall panel structure

Steel Moment resistingframe

23 With brick masonry partitions24 With cast in-situ concrete walls25 With lightweight partitions

Braced frame 26 Concentric27 Eccentric

Timber Load-bearingtimber frame

28 Thatch29 Post and beam frame30 Walls with bamboo/reed mesh and post (wattle and daub)31 Wooden frame (with or without infill)32 Stud wall frame with plywood/gypsum board sheathing33 Wooden panel or log construction

Various Seismic protectionsystems

34 Building protected with base isolation devices or seismicdampers

Other 35

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4.4 Type of FoundationType Description

Shallow Foundation Wall or column embedded in soil, without footingRubble stone (fieldstone) isolated footingRubble stone (fieldstone) strip footing XReinforced concrete isolated footingReinforced concrete strip footingMat foundationNo foundation

Deep Foundation Reinforced concrete bearing pilesReinforced concrete skin friction pilesSteel bearing pilesWood pilesSteel skin friction pilesCast in place concrete piersCaissons

Other

4.5 Type of Floor/Roof SystemMaterial Description of floor/roof system Floor Roof

Masonry VaultedComposite masonry and concrete joist

StructuralConcrete

Solid slabs (cast in place or precast)Cast in place waffle slabsCast in place flat slabsPrecast joist systemPrecast hollow core slabsPrecast beams with concrete toppingPost-tensioned slabs

Steel Composite steel deck with concrete slabTimber Rammed earth with ballast and concrete or plaster finishing

Wood planks or beams with ballast and concrete or plaster finishingThatched roof supported on wood purlins XWood single roofWood planks or beams that support clay tiles XWood planks or beams that support slate, metal asbestos-cement or plasticcorrugated sheets or tiles

X

Wood plank, plywood or manufactured wood panels on joists supported bybeams or walls

Other Earth X

Additional Comments: Roof system can be considered as flexible diaphragm.

4.6 Typical Plan DimensionsLength: 30 - 30 metersWidth: 30 - 30 metersAdditional Comments: It is for urban. For rural length is usually 6 and width 5

4.7 Typical Number of Stories1

4.8 Typical Story Height3 meters

Additional Comments: Height variation is 2.5 - 3 m.

4.9 Typical Span

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5 meters

4.10 Typical Wall DensityUrban: 35%. Rural: 20%

4.11 General Applicability of Answers to Questions in Section 4Most of the adobe housing is very similar in the rural areas. In the case of urban areas the typical plandimension may have a 20% variation from what has been specified above.

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5 Evaluation of Seismic Performance and Seismic Vulnerability

5.1 Structural and Architectural Features: Seismic ResistanceStructural/ArchitecturalFeature

Statement True False N/A

Lateral load path The structure contains a complete load path for seismic force effects fromany horizontal direction that serves to transfer inertial forces form thebuilding to the foundation.

X

Buildingconfiguration

The building is regular with regards to both the plan and the elevation. X

Roof construction The roof diaphragm is considered to be rigid and it is expected that the roofstructure will maintain its integrity, i.e.. shape and form, during anearthquake of intensity expected in this area.

X

Floor construction The floor diaphragm(s) are considered to be rigid and it is expected that thefloor structure(s) will maintain its integrity, during an earthquake of intensityexpected in this area.

X

Foundationperformance

There is no evidence of excessive foundation movement (e.g. settlement)that would affect the integrity or performance of the structure in anearthquake.

X

Wall and framestructures-redundancy

The number of lines of walls or frames in each principal direction is greaterthan or equal to 2.

X

Wall proportions Height-to-thickness ratio of the shear walls at each floor level is: 1) Lessthan 25 (concrete walls); 2)Less than 30 (reinforced masonry walls); 3)Less than 13 (unreinforced masonry walls).

X

Foundation- wallconnection

Vertical load-bearing elements (columns, walls) are attached to thefoundations; concrete columns and walls are doweled into the foundation.

X

Wall-roofconnections

Exterior walls are anchored for out-of-plane seismic effects at eachdiaphragm level with metal anchors or straps.

X

Wall openings The total width of door and window openings in a wall is: 1) for brickmasonry construction in cement mortar: less than 1/2 of the distancebetween the adjacent cross walls; 2) for adobe masonry, stone masonryand brick masonry in mud mortar: less than 1/3 of the distance between theadjacent cross walls; 3) for precast concrete wall structures: less than 3/4 ofthe length of a perimeter wall.

X X

Quality of buildingmaterials

Quality of building materials is considered to be adequate per requirementsof national codes and standards (an estimate).

X

Quality ofworkmanship

Quality of workmanship (based on visual inspection of few typical buildings)is considered to be good (per local construction standards).

X

Maintenance Buildings of this type are generally well maintained and there are no visiblesigns of deterioration of building elements (concrete, steel, timber).

X

Other

Additional Comments: Wall openings are most true in the rural and may be false in urban.

5.2 Seismic FeaturesStructural Element Seismic Deficiency Earthquake-Resilient Features Earthquake Damage PatternsWall There is a lack of dependable joints

among walls, especially at the top ofwalls. This causes adjacent walls toopen up during an earthquake.

Damages due flexural and sheareffects.

Frame (columns,beams)Roof and floors There is inadequate vertical and

horizontal load transfer mechanism fromroof to walls.

Total and partial collapse of the roof dueto material degradation and loss ofsupport from walls.

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5.3 Seismic Vulnerability RatingVulnerability

High (Very PoorSeismicPerformance)

Medium Low (ExcellentSeismicPerformace)

A B C D E FSeismic

Vulnerability Class0 >

0 - probable value< - lower bound> - upper bound

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6 Earthquake Damage Patterns

6.1 Past Earthquakes Reported To Affect This ConstructionYear Earthquake Epicenter Richter magnitude(M) Maximum Intensity (Indicate

Scale e.g. MMI, MSK)1982 Pacific Ocean 7.2 (MMI) VII1965 San Salvador 6 (MMI) VIII1951 Jucuapa/ Chinameca 6 (MSK) VIII1936 San Vicente 6.1 VII-VIII (SIEBERG)

Additional Comments: 1986, San Salvador, 5.4 (MMI), VIII El Salvador had two big earthquakes at thebeginning of 2001. The first one was on 13 January 2001 with its epicenter located in the Pacific Oceanand with magnitude Mw= 7.7, with a maximum estimated intensity of VIII (MMI). The second onehappened on 13 February 2001 with epicenter at San Juan Tepezontes and Mw= 6.5; the estimatedintensity was VIII in some places, however in many of the affected areas its intensity was VII (MMI). Oneof the most important features of these two EQ is that they destroyed adobe housing in many placesthroughout El Salvador.

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7 Building Materials and Construction Process

7.1 Description of Building MaterialsStructural Element Building Material Characteristic Strength Mix Proportions/ Dimensions CommentsWalls Adobe Brick 0.25 kg/cm² (Shear) 13:4:3 (sand:lime:clay) 400

mm X 200 mm X 150mmFoundations Mortar 1:2 (soil: straw)Roof and floors Wood Tiles

7.2 Does the builder typically live in this construction type, or is it more typicallybuilt by developers or for speculation?The builder typically lives in this construction type.

7.3 Construction ProcessFirst of all, the builder hydrates the adobe mixture, composed of 65% sand, 20% lime and 15% clay. Thewater volume could be 1/3 of the whole mixture volume. Bricks are made by placing this mixture intomolds measuring 40 cm X 20 cm X 15 cm. After 3 days, the bricks are removed from the molds and driedfor four weeks. Meanwhile, the site where the structure will be erected is leveled. Once this step iscomplete, excavation for the foundation begins. The width of the excavation is one and a half times thewidth of the wall. Both stone and mortar are placed into the hole; this will be the foundation. After thefoundation is finished, the walls begin to be erected up to 2.5 m. It has to be noted that maximum heightper construction day must be 1 m to avoid crushing of the walls due to its own weight. When walls reach2.5 m, approximately, the roof is built. Wood purlins are place on top of walls spaced 20 cm betweenpurlins. Later tiles or steel sheets are placed.

7.4 Design/Construction ExpertiseThere is some experience to build this construction type; however, the work force is not trained.

7.5 Building Codes and StandardsYes No

Is this construction type addressed by codes/standards? X

Title of the code or standard: Norma para la Contrucción de Viviendas. An additional comment: Adobehousing is addressed by El Salvador's 1994 Building Code in an appendix; however, it givesrecommendations about building better adobe housing without imposing enforcement.Year the first code/standard addressing this type of construction issued: 1994When was the most recent code/standard addressing this construction type issued? 1994

7.6 Role of Engineers and ArchitectsGenerally, neither engineers nor architects have a role in the design, or construction of this housing type.

7.7 Building Permits and Development Control RulesYes No

Building permits are required XInformal construction XConstruction authorized per development control rules X

7.8 Phasing of ConstructionYes No

Construction takes place over time (incrementally) XBuilding originally designed for its final constructed size X

7.9 Building Maintenance

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Who typically maintains buildings of this type?BuilderOwner(s) XRenter(s)No one XOther

7.10 Process for Building Code EnforcementN/A

7.11 Typical Problems Associated with this Type of ConstructionThe biggest problem of this type of construction is water due to weathering. Adobe has be protectedagainst water.In addition, it has low resistance against seismic excitation, because of its very high mass-to-strengthratio.

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8 Construction Economics

8.1 Unit Construction Cost (estimate)Rural: US$ 15 /m²Urban: US$ 30 /m²

8.2 Labor Requirements (estimate)Rural: 1.5 months using two people (including time for the mixture to be hydrated).

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9 Insurance

9.1 Insurance IssuesYes No

Earthquake insurance for this construction type is typically available XInsurance premium discounts or higher coverages are available for seismicallystrengthened buildings or new buildings built to incorporate seismically resistantfeatures

X

9.2 If earthquake insurance is available, what does this insurance typicallycover/cost?N/A

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10 Seismic Strengthening Technologies

10.1 Description of Seismic Strengthening ProvisionsType of intervention Structural Deficiency Description of seismic strengthening provision usedRetrofit(Strengthening)

Walls: There is lack of dependablejoints among walls, especially at the topof walls. This causes adjacent walls toopen up during an earthquake.

Collar Beam or Lintel Band: This feature ties the walls together.Buttresses: This feature helps to retain the integral action of walls andfacilitate the connection of collar beams with each other. Vertical andHorizontal Reinforcement using bamboo: This features tries to providereinforcement similar to that for concrete structures. Adobe bricks haveto be molded appropriately to use this kind of strengthening technique.

Roof: Very heavy elements. Sheets of metal: Use this feature instead of clay tiles

10.2 Has seismic strengthening described in the above table been performed indesign practice, and if so, to what extent?Yes, it has. However, It is not widely used. It has been done as a test in some rural communities.

10.3 Was the work done as a mitigation effort on an undamaged building, or asrepair following earthquake damage?It was done as a test.

10.4 Was the construction inspected in the same manner as new construction?No, it was not. These houses did have supervision.

10.5 Who performed the construction: a contractor, or owner/user? Was anarchitect or engineer involved?An ONG.

10.6 What has been the performance of retrofitted buildings of this type insubsequent earthquakes?Very good, nothing happened to them. However, they are located in an area that was not as affected bythe recent earthquakes.

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11 ReferencesAlvarez G., S de J. Informe técnico sobre aspectos sismológicos del terremoto en El Salvador del 19 dejunio de 1982. Dpto. De Sismología, Centro de Investigaciones Geotécnicas, San Salvador, 1982.

Ambraseys, N.N., Bommer, J.J, Buforn, E, Udias, A., The earthquake sequence of May 1951 at Jucuapa,El Salvador, Journal of Seismology (in press) 2000, pag 1-17, Netherlands.

Harlow, D. H., White, R.A., Rymer, M.J., Alvarez, S., The San Salvador Earthquake of 10 octuber 1986and its historical context, Bulletin of the Seismological Society of America, Vol 83, #4, pp1143-1154,August 1993.

Lara G., M.A. The El Salvador earthquake of June 19, 1982. EERI Newsletter, vol. 17, no. 1, 87-96, 1983.

Levin, S.B. The Salvador earthquakes of December, 1936. Bulletin of the Seismological Society ofAmerica, vol. 27, 377-407, 1937.

Norma Especial para Diseño y Construcción de Viviendas. Reglamento para la Seguridad Estructural delas Construcciones. Ministerio de Obras Públicas. San Salvador. 1994.

Rosenblueth, E, Prince, J., El temblor del San Salvador, 3 de mayo de 1965: Ingeniería Sísmica, PrimerCongreso Nacional de Ingeniería Sísmica, Guadalajara, 1965.

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12 ContributorsName Manuel A. Lopez Julian Bommer Gilda BenavidezTitle Engineer Doctor ArchitectAffiliation UES Imperial College UESAddress Escuela de Ingeniería Civil.

Universidad de El Salvador.Final 25 Av. Norte.

Department of Civil andEnvironmental Engineering.Imperial College of Science.South Kensington

Escuela de Ingeniería Civil.Universidad de El Salvador.Final 25 Av. Norte.

City San Salvador London San SalvadorZipcode SW7 2BUCountry El Salvador United Kingdom El SalvadorPhone 503-226-1846 +44-20-7594-5984 503-226-1846Fax 503-225-2506 +44-20-7225-2716 503-225-2506Email [email protected] [email protected] [email protected]

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13 Figures

FIGURE 1: Typical Building

FIGURE 2: Key Load Bearing Elements

FIGURE 3A: Plan of a Typical Building

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FIGURE 3B: Plan of a typical rural dwelling

FIGURE 4A: Critical Structural Details-An illustration of wood beams supporting clay tiles and roof-wallsconnections

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FIGURE 4B: Wall connections

FIGURE 5A: An Illustration of Key Seismic Features and/or Deficiencies

FIGURE 5B: Deficient bedding of lintels

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FIGURE 6A: Damage to an adobe house in the 1936 San Vincente earthquake

FIGURE 6B: Damage to adobe houses in the 1936 San Vincente earthquake

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FIGURE 6C: Damage to an adobe church in the 1999 Apastepeque earthquake

FIGURE 6D: Wall damage (corner separation) in the 1999 Apastepeque earthquake

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FIGURE 6E: Damages in the town of Juayua due to the January 13, 2001 earthquake

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FIGURE 6F: Damages in the city of Cojutepeque due to the February 13, 2001 earthquake

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FIGURE 6G: The San Jose church, Cojutepeque, damaged in the 13 February 2001 earthquake

FIGURE 7A: Illustration of Seismic Strengthening Techniques

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FIGURE 7B: Seismic Strengthening: Vertical and Horizontal Reinforcement

FIGURE 7C: Seismic Strengthening : Wall Buttresses

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